Terrain

Terrain is what geography is made of. It also has levels of abstraction, matching the needs of the thematic levels. Someone designing a region might decide to place a forest; someone designing an area might decide to place a wood; someone designing a wood might decide to place a tree. Terrain is the paint that depicts the image a designer wants to convey.

The different types of terrain that are available to a virtual world depend on that world, of course. Swampland isn’t necessary for a virtual world set entirely indoors, for example. Tempting though it is to go straight to an atlas and look at the symbols it uses, there are more scientific ways of determining terrain that allow for more realistic tangible effects. For a generic, outdoors, continent-scale kind of virtual world, the following dimensions are likely to be more useful:

• Elevation

• Surface geology (rock, soil, water, sand, and so on)

• Vegetation (none, grass, scrub, cultivation, trees, and so on)

• Cover (none, snow, ash, and so on)

• Volume (air, water, mist, and so on)

Thus you can have a hill, a forested hill, a snow-covered, forested hill, and so on. The particular types of forest would depend on the level of abstraction (jungle, mangrove swamp, pine, oak, whatever).

Explicitly representing each layer allows for a virtual world to give different terrains different properties. Graphical worlds benefit the most from this as they need the texture maps, but they can use them for other things, too (movement speed, footprints/footfalls, ambient sounds). However, even textual worlds can profit from giving rooms a terrain property: Trivially, if you drop a glass bottle on a paved road, it’ll shatter; if you drop it on a sandy beach, it won’t. Multi-layered terrain will also allow you to spot incongruities, such as underwater snow, but to be honest anyone stupid enough to do something like that is going to be too stupid to check for it anyway.

Ah, yes, weather…

The first time I went to San Diego, U.S. customs hauled my bag out of the X-ray machine and made me open it because they couldn’t figure out what I had in it. The object perplexing them turned out to be my umbrella.

I’m from England. We have weather in England. Weather affects terrain. Calm seas can become rough, trees in forests can sway, snow can turn to slush, grassland can become marsh, streets can turn to rivers, hail stones the size of golf balls can appear with no warning in mid-July and set off the alarms of every car parked within a square kilometer ¹. A persistent world with a climate appropriate to its geography is more believable than one that’s the same the whole year round ². You don’t need a sophisticated model to decide the prevailing winds, the temperature, and therefore the cloud cover and likely precipitation. Just because it’s always blazing sunshine where you live, that doesn’t mean it should be like that in your virtual world. Those lush green pastures have to get their water from somewhere.

The second time I went to San Diego, I left my umbrella behind. It rained so hard it stripped the paper off billboards. The locals were unfazed, as it had been forecast for two weeks. Augh!

Using a systematic approach to terrain makes moderating the effects of weather much easier. It has another, equally nice feature, which although not yet used a great deal could nevertheless be the answer to some designers’ prayers: implicit terrain.

In Lord of the Rings, all the action takes place in just a few regions. Vast swathes of Middle Earth are not affected by the conflict to any great degree. If you were designing a virtual world in this setting, you’d want to ignore those places the players weren’t going to be interested in and concentrate on those they were. Unfortunately, the result would be rather patchy. In players’ minds, maps should at the very least be rectangular; if they’ve read Lord of the Rings, they’d expect the virtual world to match the maps in the books, too.

Content costs money. Even mundane content costs money. There may only be one or two sites of interest in the Misty Mountains, but if the entire map were being represented virtually, then some designer still has to place every tree on every slope leading to every jagged peak in the whole range. That’s a lot of effort, just to pacify the occasional player who wanders by.

The overall map shows what the general terrain in a region is, even down to the area level. It’s only when the map has to be realized as actual polygons that its creation becomes tedious. This is where implicit terrain comes in.

Implicit terrain uses a guiding terrain type (that of its area) plus a random number seed (based on its co-ordinates) to generate actual terrain on-the-fly. When a player enters an area, only then is the content for it created. Any changes made by the player (for example, burying treasure) are recorded so as to supersede the implicit definition, but everything else can be discarded after the player leaves. It’s less efficient in implementation terms than an explicit representation, but more than makes up for this in designer efficiency. Random mobiles can be created for an area to spice it up, but on the whole they are only there because players are passing through and would notice if they weren’t. Having terrain that’s defined in layers makes for easier fractal area generation than terrain that’s defined by natural language terms ³.

Most designers won’t have this problem of a map that’s too big. However, that doesn’t mean implicit terrain can’t be of use to them. In particular, it can step in to generate content whenever a player walks off the map. Players can be dissuaded from going too far by including ever-tougher mobiles, but then it doesn’t really matter if they do go on forever—the geography can always be generated for their co-ordinates. It won’t be compelling content, of course, but it removes the problem of clichéd boundaries. If you’re doing a virtual world set in space and you want an infinite universe, well, you can have one.